In facilities such as power substations handling high voltage, there are generally used gas-insulated apparatuses such as, for example, gas-insulated switchgears, gas-insulated buses, and gas-insulated transformers, in which a conductor to which high voltage is applied is insulated by gas. In the gas-insulated apparatus, a high-voltage conductor to which high voltage is applied is housed in a hermetically sealed metal container filled with insulating gas, and the high-voltage conductor is supported by an insulator.
In such a gas-insulated apparatus, it has been known that, if the metal container has a defective portion with a contact failure or with an intruded metal foreign particle, partial discharge occurs from this defective portion. Leaving the partial discharge in the gas-insulated apparatus as it is would lead to dielectric breakdown before long, which is likely to develop into a serious accident. Therefore, it is important to detect the partial discharge at an early stage and prevent the occurrence of the serious accident by taking measures such as the repair of the defective portion. As a preventive maintenance technique in insulation diagnosis of the gas-insulated apparatus, there has been proposed a detector detecting the partial discharge inside the gas-insulated apparatus.
As discharge detectors detecting the partial discharge inside the gas-insulated apparatus, there have been known those detecting the partial discharge by sensing electric current, electromagnetic waves, sound, vibration, light, and the like. Among them, a device sensing electromagnetic waves generated due to the partial discharge to determine the presence/absence of the partial discharge has been drawing attention because of its high detection sensitivity, high S/N ratio, wide detection range, and so on. Since the electromagnetic waves accompanying the partial discharge include frequency components with frequencies in a wide range from several tens MHz to several GHz, a method of detecting electromagnetic wave signals in UHF band (300 MHz to 3 GHz) that are relatively easily detected has come into the mainstream.